Thread generating cutter



I Nov. 24, 1931. I E. w. MILLER I 1,833,255

THREAD GENERATING CUTTER Original Filed July 14, 1928 '2 Sheets-Sheet 1Nov. 24, 1931. w, MILLER ,833, 5

READ

' Original Filed July 14, 1928 2 S eeee s-Sneet 22 /a 20 34 /6 /2 2249,20 24 my 22 2a 4&6: I 2f I Patented Nov. 24, .1931

-UNITED STATES PATENT F ICE] bwm w. MIiLEa'or SPRINGFIELD, VERMONT,ASSIGNOR To THE rEImows om swan. comm, or SPRINGFIELD, VERMONT, ACORPORATION or VERMONT THREAD GENERATING CUTTER Application filed July14, 1928, Serial No. 292,871. Renewed October 16, 1931.

The present invention relates to cutters designed primarily'forgenerating threads 1n a form conjugate to the teeth of the gear or wormwheel with which suchthreads are intended to cooperate in use, Thethreaded articles for which, in the making, cutters of the type of myinvention are used, are machine rack tooth designed to mesh with a gearelement. It is within my contemplation also to apply such cutters to thegeneration of helical gears, using a cutter of which the number of teethis prime to the number of teeth in the gear. The cutters used forgenerating such threads have teeth analogous to the-teeth of a gearconjugate to the work piece but with modifications adapting them toserve as metal cutting instruments and to be sharpened .and used afterrepeated sharpenings. This type of cutter is not new, and indeed one ofthe type is shown in connection .witha thread generating machine in myprior Patent No. 1,461,219, dated July. 10, 1923,to which reference isdirected for further explanation. The new step of this invention is animprovement in cutters of the type thus indicated by which certain wellrecognized defects of the old cutters of this type have been'correeted.The principles and advantages of my new step may best be understood andappreciated in the light of a brief descriotion of the cutterspreviously used.

The teeth of such cutters are themselves helical comformably to thehelix of the threads to be cut, in order to clear the sides of suchthreads, and are provided with cut ting edges on one end formedoriginally, and afterwards maintained in sharp condition, by grindingaway the ends of the teeth approximately in a plane perpendicular to theaxis of the cutter. Actually the end faces are ground at a slightinclination to such per pendicular plane in order to give the teeth thetop rake which is necessary to obtain the best cutting effect; but asthe deviation of the angle of top rake from the plane perpendicular tothe axis is small and causes noappreciable error in the generated threadforms, it'maybe disregarded for the purposes of. this explanation.

, The sharpening of all the cutter teeth in such a plane has the seriousobjection that it leaves the angle between one side of the tooth and theend face obtuse, wherefore the intermediate edge has poor cuttingqualities. With cutters designed for threads of the steeper pitches, thehelix angle of the teeth is correspondingly larger and the efficiency ofthe edge-at the obtuse angle correspondingly less than with cuttersof-less helix angle.

The opposite edge, that of the acute angle of the tooth, however, ishighly eficient and requires only relatively infrequent sharpening inorder to maintain it in good cutting condition.

The best method heretofore known for overcoming this highlyunsatisfactory condition has been to grind a notch in the end of eachtooth adjacent to the obtuse side with one face of the notch at aslightly acute angle to this side but this practice has not been whollysatisfactory because such notches can be out only by the corner of agrinding wheel between its circumferential face and an end face, and itis difficult to keep such corner sufficiently sharp. rapidly and unlessthe wheel is carefully The corner breaks away watched and frequentlytrued, it will quickly wear away so much as to make the notch cut by ita rounded groove intersecting the side of the tooth at an obtuse angleinstead of the desired acute angle. This difficulty is particularlymarked with cutters having small teeth, and is so great as to become avery serious obstacle to the maintenance anduse of such cutters. 2

According to the present invention I have overcome the difficultiesabove noted by grinding the end faces of certain teeth all the wayacross in planes approximately normal to the helix angle of these teeth,but sufficiently in.- clined to the helix angle to give the desireddegree of top rake both from point to root 9; of multiple lead, andtherein,- I

- and laid in a lane;

said obtuseangle sides approximately or subcent teeth of the cutter(that is, the bounding ed es of each alternate topth space) cutting eges capable of efficiently cutting the opposite sides of the same threadbe ng formed in the work. The invention consists in the cutter havingthe novel features above named, and others relating thereto and moreparticularly pointed out in the following specification and claims. I

Having occasion in this specificat on to refer to one of the sides ofthe cutter tooth as the obtuse side or face, I will define at this pointthe meaning of obtuse as so used. The obtuse side or face of the toothis that ,which makes an obtuse angle with any plane perpendicular to theaxis of the cutter at that side of the face on whichthe substance of thetooth lies. While of course each side face of the tooth, considered onlyas a surface regardless of the body of the tooth, makes an acute angleon one side and an' obtuse angle on the other side with planesperpendicular to the axis,.I am considering as the'obtuse angle side forthe purposes of this specification only that side which, when producedtothe cutting end and intersected by the plane at the end of the cutterperpendicular to its axis, bounds the tooth on an obtuse angle.Conversely, the acute angle side of the tooth is the s1de which,extended and intersected by the end plane, bounds the corner of thetooth m an acute angle. I shall use these terms with reference not onlyto those teeth of the cutter which are actuallybounded on the'end by theend plane of the cutter, but also as to those teeth which are modifiedaccordin to the res t. nt' b bein truncate at their p en mve Ion y g.the end faces 18 alternate with teeth 15a ends on inclined planes.

In the drawingsfurnishedherewith I have shown a cutter embodying theprinciples of this invention designed for cutting threads action of thecutter in finishing the generated threads; n

Fig; 6 is adevelopment view in elevation of a part of the cutter,representing the teeth as though unwrapped from the base Fig. 7 is aragmentary diagrammatic cross section illustratmg the cutting action ofthe tool, being taken on line 7'( p of Fig. 8;

Fig. 8 is a sectional view of the work piece and tool in cooperativerelation,'taken on a plane perpendicular to the axis of the work ,andincluding theaxis of the tool.

by two components, one bein plemental to that of the woi k,

cylinder the meaning 0 Like reference characters designate the sameparts wherever they occur in all the figures.

which thread generating cutters of-the type of my improved tool operate.10 represents the work piece adapted -to rotate about its axis 11 in thedirection of the arrow; and 12 represents the cutter arranged to rotateabout Reference is first directed to Fig. 8 for explanation of theprinciples according to its axis 13, 14, and having teeth 15. The

necessities of accurateand symmetrical thread generation demand that thecutting edges lie and operate as nearly as may be in a plane radial tothe axis. The line 16, 17 represents such a plane. The cutter isarranged with its axis 13, 14' perpendicular to this plane and the endfaces of its teeth are all ground so that at least one edge isapproximately or substantiallyin this plane. 18 represents theend facesof the teeth 15, which are shown as diverging from the plane 16, 17suflic-ientl'y'to form the desired top rake in the radial direction. Inoperation the work and cutter are both rotated about their axes, and inaddition there is a. relative movement of translation between them inthe direction of the axis of the Work. The speed of rotation of thecutter is determined the speed coma worm'and gear couple, and the otherbeing that of a gear rolling in mesh with a rack at the translativespeedof the cutting travel.

, The second component is much smaller than considered as the firstowing to the fact that thefeeding travel is relatively "slow. It is goodpractice to provide for a feeding travel of about .002" 6 during eachrotation of the work. 7 In. my improved cutter the teeth 15 havinghaving end faces 18a. All the teeth are alike except in the character oftheirend faces.

side face 23. The acute angle provides top rake tangentially of thecutter.

The end faces 18a of'teeth 15a on the other hand are nearly normal tothe helix angle or helical length of the teeth, but enough in-. clinedthereto to make an acute angle, giving a desired degree'oftangential-top rake at the edge24 with the face 23 of the tooth,whichcorresponds with the face 23 of tooth 15, and

is the obtuse an le side of, tooth 15a within the definition previouslygiven. That is, this face. would make an obtuse angle with thefend planeof the cutter if wardly from the point of the tooth of anamountsubstantially equal to the top rake of the teeth 15. The face 18ais'continued entirely across the tooth a and part way across theadjoining tooth space, forming an edge 25 at its intersection with theside face 21 which is slight-1y obtuse. It is also some .w hat below theend plane of the cutter, and

on this account is less efficient as a cutting edge and less: accurate.as a generating medium than the edges 20 and 24.

The result is that each tooth has one excellent cutting edge and oneless eflicient edge; but these edges are on relatively opposite sides,wherefore each alternate space is bounded by two good.edges lyingsubstan tially in the cutting plane. The latter edges therefore have thegreatest possible accuracy and efiiciency, 'and they perform the finalstages of cutting the threads to finished form and dimensions.

Inother respects the cuttenteeth may be like those of the cuttersheretofore made for this class of work. The side faces of the teeth areusually involute curves generated by known methods in such fashion thatthe intersections of such faces with all planes'perpendicular to theaxis of the cutter are involutes of the same base circle. These sidefaces moreover are preferably formed with helix angles A and A,(indicated in Fig. 6), additional to the helix angle of the tooth as aWhole in order to provide side clearance in "cutting. The peripheraledges at the extremities or points of the teeth are adapted to cut andfinish the bottoms of the helical grooves between the threads generatedin the work.

The action of the cutter in the final stages is shown in Figs. -4 and5,'wherethe cutter teeth are represented in a conventional way,

and not as they actually appear in end view. But their respectiveefiicient and less eflicient edges are designated by the same referencecharacters as previously used. It is apparent from these figures, andalso from Fig-.

plished by the dimensions of the cutter teeth,

and is important, since rubbing of the obtuse angled edges on the workwould tend to break down and score the contiguous wall of the thread byscraping off fine chi s and' crowding them against said wall. 11 Fig. 4,two

.ing that with which it was of the cutter teeth are shown in cuttingposition. One of the teeth 15 'has its acute edge 20 incutting action onthe right handside of a thread a of the work piece, and thenextfollowing tooth 15a has its edge 24 in cutting action on the secondfollowing thread 0 of the work piece. The intermediate thread I), havingalready been reduced by previous cutting may-be entirely out of contactwith the cutter teeth. Assuming that the rotation of the cutter islefthand, then its movement angularly through the angle of one tooth (15in the case of a 24 tooth cutter) accompanied by a correspondingrotation of the work, brings the tooth 15a, into the position previouslyoccupied by the tooth 15, and the following tooth, which mayhere be,distinguished by the numeral 15b, although it is identical in characterwith the tooth 15, occupies the position previously held by 15a. Thethread I) meanwhile advances to the po sition formerly occupied by a,and c advances to'the position previously occupied by b, and. becomesengaged upon both faces atonce by the flanking acute angle edges 24 and20' of teeth 15a and 15b. I i

This action goes on continuouslyfleach alternate thread being engagedfirst on its advancing side by the acute angle edge ofone cutter toothand then engaged on its opposite side by'the acute angle edge,of themextfollowing cutter tooth. Each thread remains in contact with the samecutter tooth throughout the arc of action of the latter, and on eachfollowing rotation of the work comes into engagement with a toothfollowpreviously engaged.

ly acted on by the finish-cutting edges the number of teeth of thecutter is made prime to, that is indivisible by, the number of threadsin the work. Thus if the work has two threads, the cutter must have anodd number of teeth, if the thread is triple, the number must be notdivisible by three, and

In order that all'the threads may be equalso on. In these drawings, a 24tooth cutter is shown suited to generate a worm of five threads. Thuswith each repeated rotation of the cutter the threads which previouslypassed between obtuse angle edges come into action with the efficientacute angle edges of the cutter. In-the case of a cutter having an oddnumber of teeth, two adjacent teeth at .one location must be alike, andthese may be made either like the'tooth 15 or like the tooth 15a. Allthe other teeth, however, have the alternation between those which arefaced on the end in a plane substantially perpendicular to the cutteraxis, and those faced in planes approximatelyperpendicular to their[helix angle. This condition therefore may eneral condition not -deniedby the exception just noted in regard be considered as a to cuttershaving an odd number of teeth. 1' i i In sharpening the cutter all ofthe zteeth are ground on the ends by rotationof the cutter about itsaxis in contact with the circumference of a grinding wheel according tothe practice previously followed. The ends of the teeth 1511 are thenground by'tilting the cutter at the prescribed inclination with respectto a grinding wheel and prod-ucing a radial traverse between the cutterand grinder, with indexing of the cutter after each tooth has beensharpened. If desired, however, the teeth 15 may be sharpened in thesame manner as teeth 15a, in planes at any desired inclination to theirhelix angle.

wheel and effecting relative traverse between the grinder and cutterradially of. the cutter, as described with respect to the teeth 15a.

The teeth of both categories, 15 and 15a, may be iven therebyv the sametop rake, tangential y and radially of the cutteryor any other degreesof top ra e, whatever their helix ani gle may be.

' Important advantages result from thus sharpening or truncating thealternate teeth 1511., including time economy and practital assurance\ofsatisfactory results. 'ljime. economy follows from the fact that thesharpening operator can more quickly and easily grind the faces 18a ofalternate teeth,

which extend all the way across suchftooth and part Way across theadjacent spaces, than grind narrow notches in each tooth extendingacross only half the width of the tooth, for a cutter of any given sizeand pitch.

The grinding wheel requires less careful,

watching to be sure that its corner is not too much rounded over, andrequires less freuent truing to keep it in satisfactory condi- 't1on2'Better assurance of satisfactory edges follows from the fact that thereis no 11ability of the grinding wheel becoming so bad- ?rounded on thecorner that it would not orm each edge 24 with an acute angle, for

60 the rounding of the edge to cause such a failure would necessarily beof large radius and impossible to escape detection. A modirate roundingof the corner would do no It is to be understood that'the foregoingexplanation of the, purposes and uses to whichmy improved cutter are putis not a limitation of the scope in which I claim pro tection. On thecontrary, I claim a cutter having the characteristics herein describedfor whatever purpose it may be adapted and used, whether new knownto .meor which ma- 'be later devised. v

at I claim and desire to secure by Letters Patent is:

1. A circular cutter of the character herein set forth having aperipheral series of helical teeth of WhlCh every alternate tooth facedoff on the end-approximately in a plane perpendicular to the axis of thecutter,

and the intermediate teeth are faced OK in planes approximately normalto their helix angles.

2. A circular cutter having a peripheral series of helical teeth withcutting edges defined by the intersections of their end faces with theirside faces, the end face of one tooth making an obtuse angle with oneside face and an acute angle with the other side face, and the nexttooth having an acute angle edge at the side adjacent to the acute angleof the first named tooth and substantially in the same plane therewithperpendicular to the axis of the,cutter; the opposite edge of the lastnamed tooth being in a, 'different plane.

3. A circular cutter having a peripheral series of helical teeth withcutting edges .formed by the intersections of their end faces with theirside 'faces, certain ones of whichare truncated entirely across theirends in planes approximately normal to their helix angle, and othersterminate approximately,

in a plane perpendicular to the'axis of the cutter. v

4. A circular cutter having a peripheral series of helical teeth withcutting edges formed by the intersections of their end faces with theirside faces; .certain of said end facesbeing approximately perpendicularthroughout their entire width to the helical length of their respectiveteeth but so inclined as to make an acute angle with the obtuse angleside'of such tooth, and others being approximately perpendicular to theaxis of the cutter. 1

5. A circular generating cutter having a peripheral series of helicalteeth with cutting edges formed by theintersections between' "their endand side faces, the end face of each tooth being substantially in asingle 'plane and being so disposed that certain of the spaces betweenthe teeth are bounded on both sides by acute angle cutting edges.

6. it circular cutter for thread generation having a peripheral seriesof helical teeth with end cutting edges, the end face of each toothbeing substantially an uninterrupted plane, and theplanes of differentteeth being so differently inclined A to their respective helix anglesthat the edges flanking certain spaces between the teeth are both sharpangled cutting edges and occupy nearlythe same plane perpendicularto theaxisofthe cutter.

7. A circular cutter for thread generation having anodd number ofhelical teeth in its I periphery each formed with an ac cutting edge atone end and with the end face bounding such cuttin edge beingsubstantially an uninterrupte plane; the acute e le angled cuttingedgesof adjacent teeth being at relatively opposite sides, except as to theodd tooth, which is like the adjacent tooth 'at one side.

8. A- circular generating cutter having a peripheral series of helicalteeth, each bounded at one end by a single substantially continuous faceat such an inclination to the helix angle of the tooth as to make anacute angled cutting edge by intersection with one of the side faces ofthe tooth; such acute angled edges of adjacent teeth in repeatedalternation, facing toward one another and bounding the intermediatespace, and all being substantially in the same plane.

9. A cutter as and for the purpose set forth having helical teeth withcutting edges at one. end, said teeth being arranged in pairs with thecutting edges at the adjacent sides of the teeth of each pair formed bythe intersecw tions with such sides with end planes making acute .anglerespectively with the said adjacent sides, the opposite edges of saidteeth being obtuse angled, and the teeth having a thickness less thanthe width of the grooves to be cut in the work so that the acute anglededges only engage the sides of a rib between two grooves or segments ofgrooves, and the opposite edges of the teeth are clear of the work.

In testimony whereof I have affixed my signature.

EDWARD W. MILLER.

